Plants require Nitrogen (N) to grow. Nitrogen is abundant in its atmospheric form, N2 (nitrogen gas), which makes up 78 percent of our atmosphere. However, most plants cannot use nitrogen in this form, but N2 can be transformed into several other compounds that plants can use. The form and movement of Nitrogen through the nitrogen cycle are greatly influenced by soil bacterial action on various Nitrogen compounds and by components of the local ground water systems. These are various forms of N that relate to one another through many complex interactions of various forms of nitrogen, including: atmospheric nitrogen (N2), ammonia (NH3), ammonium ion (NH4+), nitrite ion (NO2−), and nitrate ion (NO3−). Each N form has properties that affect plant utilization of N.
Non-leguminous plants, such as grass pasture, corn, and most fruit and vegetable crops, must rely on either bacteria that live in the soil to “fix” the nitrogen from the atmosphere, or to convert nitrogen from decomposing organic matter, or to convert nitrogen from applied fertilizers into suitable useable forms of nitrogen which plants can take up through their roots. The most common forms of nitrogen that plants can use are ammonium ions (NH4+) and nitrate ions (NO3−).
Ammonium-based fertilizers are used to provide plants with N. Unfortunately, soon after application to soil, ammonium based fertilizers disassociate to form ionic components in soil water to form ammonium ions which are converted to the nitrite; nitrate forms rather quickly by nitrifying bacteria, believed to be bacteria such as nitrosomonas and nitrobacter.
Legumes for example alfalfa, clover, soybeans and peanuts, have nodules on their roots that contain bacteria that fix atmospheric nitrogen into a usable form for the plant without the need for as much, if any, nitrogenous fertilizer compared to non-leguminous plants. When ammonium sulphate solubilizes the resultant ammonium ions (NH4+), have a positive charge, and as a result attach to the negatively charged soil particles.
Nitrogen can become unavailable to plants primarily because of rapid nitrification followed by leaching in wet soils, or by washout because of heavy rainfall. This important means of nitrogen loss is by nitrate leaching. Leaching occurs when the water-soluble nitrate ion moves through the soil as water percolates downward beyond the reach of plant roots.
Another important means of nitrogen loss is through rapid denitrification. Compacted wet soils contain little oxygen and denitrifying bacteria that are active under anaerobic conditions remove the oxygen from the nitrogenous products of nitrification of ammonia, such as nitrite (NO2−) ions and nitrate (NO3−) ions for their own use, releasing N2 and/or N2O back to the atmosphere.
One of the problems with Nitrogen loss from chemical fertilizers vs. organic Nitrogen containing fertilizers are that fast release high Nitrogen fertilizers such as ammonium salts, nitrates, or urea are water soluble and are quickly assimilated by various enzymes and nitrifying bacteria, and denitrifying bacteria resulting in loss of Nitrogen by nitrate leaching to aquifers, by wash outs as surface run-off due to heavy rains, or by quick release of Nitrogen containing gases or greenhouse gases.
There has been much progress to slow the breakdown by bacteria of nitrogenous fertilizers, resulting in a number of commercial categories being developed for these slow release N or controlled release N fertilizers such as sulphur coated ureas, resin coated nitrogenous products, slow release urea formaldehyde nitrogen fertilizers, and organic fertilizers such as fish meal.
Each of these slow release or controlled release fertilizers have their own disadvantages. For example, sulphur coated urea fertilizers slow the availability of nitrogen, but once the sulphur type combination wax coating is gone the release of the underlying urea Nitrogen is rapid. Resin or compound coated fertilizers may in fact be too slow to release nutrients over the growing season. Slow release urea formaldehyde fertilizers are designed to give two stages of Nitrogen release, rapid release from free urea, and timed release because of condensation reaction of part of the urea with formaldehyde, but the final timed stage may release free formaldehyde emissions. Other slow release Nitrogen urea fertilizers produced by unique polymerization or condensation of urea with an aldehyde, normally formaldehyde, are crotonylidinediurea (CDU) and isobuitlidene diurea (IBDU). Organic fertilizers such as protein based fish meal are expensive and not available for large scale commercial use.
In addition to the above commercial categories for slow or controlled release of Nitrogen fertilizers, a number of chemicals have been found to inhibit nitrification of nitrogenous fertilizers. Nitrification inhibitors restrict the microbiological oxidation of ammonium ions to nitrate ions thereby reducing the loss of N from nitrification, by leaching, and by early denitrification. The literature on nitrification inhibitors is very extensive as outlined by Patra in U.S. Pat. No. 6,336,949, Jan. 8, 2002, wherein it was discovered essential oils inhibited the hydrolysis of urea by urease enzymes, and hence retarded nitrification of the urea. Another known nitrification inhibitor is nitrapyrin (2-chlor-6-trichloromethyl pyridine). Following its invention, a series of chemicals, including BHC, sodium azide, sodium chlorate, dicyandiamide (DCD), thiourea AM (2-amino-4 chloro-6 methyl pyridine), ATC (4 amino-1, 2,4 triazole), and N-serve have also been identified as nitrification inhibitors (Sahrawat et al 1989, Adv. Agrron. 42:279-309). DCD (Dicyandiamide), a chemical normally derived from coal by-products, is a commercially sold as an ammonical nitrogen nitrification inhibitor. However, it is difficult to source, and in short supply because there are few manufacturers of DCD outside of China and Germany. EP patent publication 0030019242 describes use of hydrolysable tannins as a potential nitrification inhibitor in fertilizer, however, hydrolysable tannins are expensive and difficult to source commercially.
Tannins, sometimes referred to as polyphenols, are naturally occurring polyphenolic polymers extracted from tannin containing vegetable, plant and forestry products. Tannic acid, a derivative of tannin, is known to have a strong effect on bacteria in the medical field. Tannins are classified as hydrolysable tannins and condensate tannins. Hydrolysable tannins are constituted by galic acid ester compounds and ellagic acid ester compounds with a sugar, usually glucose, and they can be hydrolysed by acids into monomeric compounds and enzymes. Condensate tannins, which are called polyflavanoids, and sometimes referred to in the present specification as condensed tannins, have a completely different chemical structure. They are comprised of a polyhydroxylflavonol polymer group, with carbon to carbon bonds between their sub units.
Hydrolysable tannins, such as those found in the leaves of certain shrubs such as tea, were presumed to have nitrogen nitrification inhibitory properties by earlier investigators. Tea waste has been reported to retard nitrification (Sahrawat et al 1989, Adv. Agron. 42:279-309). Experimental soil application of tea waste from tea production tables in tea factories did inhibit some urea nitrogen nitrification, but fared inefficient compared to N-serve, or neem cake, S. M Arafat, Pakistan Journal of Bilogical science 2(4): 1184-1187, 1999.
Bargiachhio et al in European patent application EP 20030019242 teaches methods for using organic hydrolysable tannin extracts in agriculture, such methods including water leaching of tannins and sugars out of wood based matter, drying the leachate, and using the dried leachate to coat fertilizers in a rotary drum, or using the extracts to add to solution and suspension fertilizers, or for use and application by fertigation, or fertilizing through irrigation systems. However, Bargiachhio uses natural sugars, starch, lactose, bran, or carbohydrates in the taught fertilizers, and therefore the methods used by Bargiachhio can actually cause the quicker onset of denitrification of nitrates to greenhouse gases more quickly because denitrification bacteria require additional carbon to multiply. In addition, Bargiachhio teaches use of hydrolysable tannins, and the use of high ratios of tannin to nitrogen, resulting in high cost.
Most other nitrification inhibitors currently known or in use are synthetic chemicals, expensive, and have undesirable environmental side effects.
Hence there is a need for a natural, inexpensive nitrification inhibitor, and/or a fertilizer having such an inhibitor.